Heretofore, a gas barrier film obtained by using a plastic film as a base material and forming an inorganic thin film made of aluminum oxide, magnesium oxide or silicon oxide on the surface of the plastic film using a vacuum deposition method, a sputtering method, a CVD method or an ion plating method has widely been used in packaging applications so as to package articles requiring barrier of various gases such as steam and oxygen, and to prevent deterioration of foods, industrial products and drugs. Intense interest is shown towards, in addition to packaging applications, applications of the gas barrier films to a portion of a transparent conductive sheet used in liquid crystal display, solar battery, electromagnetic wave shielding, touch panel, substrate for EL, and color filter. The gas barrier film is excellent in printability because of excellent wettability of an inorganic thin film, and is therefore widely used as a printed packaging material.
Various improvements and studies have been made for the purpose of preventing deterioration of gas barrier properties of the gas barrier deposited plastic film, and there has been known a method of improving gas barrier properties while maintaining transparency by subjecting the deposited film to a water absorption treatment and a heat treatment (see, for example, Japanese Unexamined Patent Application, First Publication No. Hei 2-299826) and a method of forming a coated layer made of various polyurethanes, various polyesters, or a mixture of polyurethane and polyester on the deposited surface (see, for example, Japanese Unexamined Patent Application, First Publication No. Hei 2-50837). Also there have been known gas barrier laminated films obtained by coating a gas barrier resin such as a mixture of a water soluble polymer and a metal alkoxide, a vinylidene chloride-based copolymer or an ethylene vinyl alcohol copolymer (hereinafter referred to as “EVOH”) on the deposited surface (see, for example, Japanese Unexamined Patent Application, First Publication No. Hei 8-267637 and Japanese Unexamined Patent Application, First Publication No. Hei 7-80986).
With respect to paramagnetic defects in silicon oxide, Pb center (g value: 2.003) due to defects of an interface between Si and SiO2 and E′ center (g value: 2.001) due to defects of oxygen vacancy in SiO2 as observed by an electron spin resonance method (ESR method) have been known (J. Appl. Phys., Jpn. 70, 852 (2001)), and there has been proposed a gas barrier film comprising silicon oxide formed by a CVD method in which radical density of the E′ center observed by the ESR method is specified (see, for example, Japanese Unexamined Patent Application, First Publication No. 2002-192646).
However, gas barrier properties of a film comprising an inorganic thin film layer formed thereon described in Japanese Unexamined Patent Application, First Publication No. Hei 2-299826, Japanese Unexamined Patent Application, First Publication No. Hei 2-50837, Japanese Unexamined Patent Application, First Publication No. Hei 8-267637 and Japanese Unexamined Patent Application, First Publication No. Hei 7-80986 are still considered to be insufficient and thus a film having excellent gas barrier properties has been required.
In a gas barrier film comprising a silicon oxide thin film formed thereon described in Japanese Unexamined Patent Application, First Publication No. 2002-192646, radical density of the E′ center is defined. However, the silicon oxide formed by a vacuum deposition method has a structure comprising the Pb center as a main component, and it was found to be difficult to specify the structure by the E′ center so as to obtain excellent gas barrier properties by radical density.